There are two completely different definitions of Cayley numbers. The first type Cayley numbers is
one of the eight elements in a Cayley Algebra, also known as an Octonion. A typical Cayley
number is of the form

where each of the triples , , , , , , behaves like the Quaternions . Cayley numbers are

The second type of Cayley number is a quantity which describes a Del Pezzo Surface.

**References**

Conway, J. H. and Guy, R. K. ``Cayley Numbers.'' In *The Book of Numbers.* New York: Springer-Verlag,
pp. 234-235, 1996.

Okubo, S. *Introduction to Octonion and Other Non-Associative Algebras in Physics.*
New York: Cambridge University Press, 1995.

© 1996-9

1999-05-26